Although a number of differing orthodontic techniques exist, the majority of orthodontists in practice in the United States, at this time, utilize one of two basic orthodontic therapy techniques in their treatment of patients. These basic techiques are the "light-wire" technique and the "edgewise" technique. Light-wire appliances were first designed and presented to the profession by an Australian orthodontist, R. P. Begg, who introduced the idea of differential force control. Since some types of tooth movements evoke more tissue resistance than others, and some movements occur faster than others, Begg reasoned that by selectively choosing the movements required and relating the reciprocal reactions properly, tooth movement might be accomplished in orderly manner. The Begg light-wire technique is characterized by a number of significant features. Brackets are fixed to all of the teeth of the patient anterior to and including the first molars. Archwires are round in cross-section and provide archform and leveling of the teeth. Archwires are loosely pinned to the bracket and are not ligated. The Begg brackets provide a single point contact with the archwire to minimize friction and permit the teeth to slide, rotate, tip and torque freely. For purposes of this invention, tipping movement of the teeth is defined as rotation of the long axis of a tooth in the mesia-distal direction. Torque movement means rotation of the long axis of a tooth in a buccal-lingual direction. Rotation is defined as movement of a tooth about its long axis in a mesial-distal direction. Tip, torque and rotation are accomplished by auxiliaries and not by the fit between the archwire and bracket as in the edgewise technique. Extra oral anchorage is not used. Reciprocal anchorage is provided for by selectively utilizing teeth posterior to extracton sites to retract teeth anterior to the extraction sites with intra and inter maxillary elastics. The light-wire appliances are now several and varied from the original design, although all employ sophisticated concepts in theories of tooth movement and anchorage control. Standard light-wire therapy does not utilize extra-oral traction, frequently involves extraction of teeth and typically employs more auxiliaries than conventional edgewise therapy.
The most widely utilized orthodontic therapy technique in this country, and the technique to which this invention is directed, is the "edgewise" technique, which was brought to the industry by Dr. Edward H. Angle. It should be understood, however, that this invention is also applicable to other orthodontic techniques such as the multi-phase and twin wire edgewise techniques, for example. In the beginning stages of edgewise therapy, archwires of circular cross-sectional configuration are employed. The greater flexibility of the round wire permits greater raange of movement of malposed teeth with less force to the teeth. For secondary and finishing therapy, the edgewise technique typically incorporates a multibanded precision appliance consisting of a labial archwire of rectangular cross-section that is ordinarily of greater dimension at the sides than at the edges thereof. The archwire is fitted and ligated with metal ligature wire, or ligature elastics, or any other suitable form of mechanical retention, into precision mating horizontal archwire slots that are formed in brackets on all of the permanent teeth including first molars and frequently second molars. The archwire terminates in buccal tubes each having a rectangular passage through which the ends of the rectangular archwire extend. The archwire, which may be composed of stainless steel or precious alloy, is typically positioned with its narrow dimension or edge lying against the labial and buccal surfaces of the teeth. This feature gives the technique its name "edgewise." The edgewise technique makes control possible in all directions and any individual tooth may be moved simultaneously in three directions; for example, an incisor may be moved lingually, distally and rotated around its long axis with one adjustment of the archwire. The rectangular cross-sectional configuration of the archwire permits it to be twisted to a desired extent and, being of spring-like nature, the twisting forces will be applied through the archwire to the teeth, thereby inducing a torquing movement of the teeth as the archwire untwists due to spring action and returns to its normal untwisted configuration. The brackets are precision milled to a rectangular shape so that the orthodontist can select precision milled archwires to fit as precisely as desired. Tip, torque and rotation are accomplished by the fit between the archwire and bracket. Extra oral anchorage may or may not be used as desired. Reciprocal anchorage can be provided by extraction of teeth and selectively utilizing teeth posterior to extraction sites to retract teeth anterior to the extraction sites with intra and inter maxillary elastics and/or closing loop archwires. This invention is specifically directed to the edgewise technique and more specifically concerns an orthodontic appliance system that integrates specific advantages that are afforded by edgewise appliances of single and twin ligating capability.
Single tie wing brackets for the edgewise technique typically incorporate a base structure which has a precision active archwire groove that receives a rectangular archwire. A pair of ligating tie wings extend from the bracket base on opposite sides of the precision archwire slot. These tie wings are typically centered with respect to the bracket structure and are therefore intended to be positioned in substantially centered mesio-distal relationship with the facial surface of the tooth to which the bracket is secured. A ligature wire or elastic is looped over each of the tie wings and is passed over the archwire at each end of the slot, thus securing the archwire firmly in its precision slot.
Single brackets provide maximum efficiency in the application of tipping and torquing of teeth but are minimally efficient in rotational control. Initially, rotational control was accomplished by soldering or welding eyelets at the extreme mesial or distal of the band attached to the tooth. The orthodontist could ligate the eyelet to the archwire, pulling that surface closer to the archwire and causing the tooth to rotate about the centrally located bracket. This is a cumbersome and inefficient method of rotational control.
Subsequently, fixed or flexible rotation levers, projecting mesially and distally, were added to the centrally located single bracket. Thus, a rotated tooth would have the rotation wing projecting more facially than the bracket. The archwire would touch the rotation wing and, as the wire is ligated into the bracket, cause the tooth to rotate about the bracket. The rotation lever is adjustable to project more or less to the facial as desired. This permits the orthodontist to select the amount of rotation desired by adjusting the rotation lever rather than adjusting the archwire.
The disadvantage of the rotation lever approach to tooth movement is evident in the initial stages of treatment. The archwire will not touch the rotation lever if a tooth is tipped and rotated severely and will prevent either action from occurring unless the archwire is adjusted to strike the rotation lever when ligated. Thus, initial archwire insertion can be inefficient and require more expertise to ligate.
Twin brackets were introduced to alleviate the inefficient rotation effectiveness of the single bracket. Instead of one centrally located bracket, two brackets were placed at the mesial and distal of the tooth. Thus, when each bracket is ligated to the archwire, the facial surface of the tooth will align itself with the archwire, rotating the tooth.
One of the principles of rotation in orthodontics is over-correction of the original problem to compensate for the rebound or relapse tendency. This is especially indicated for rotated teeth. Twin brackets do not have the capacity for over-rotation. For over-rotation with twin brackets, the archwire must be bent or some auxilliary must be added to push the mesial or distal portion of the bracket away from the archwire. Further, single edgewise brackets, without rotation levers, are also lacking in over-rotation control capability which will be discussed in more detail hereinbelow.
One of the more important advantages of single brackets is the advantage that is afforded by the active length of archwire existing between the points of connection to adjacent brackets. This is known as "interbracket width." Since the connecting point between adjacent single brackets is established at substantially the center of the adjacent teeth, the archwire length, and thus the interbracket width, extends to points near the centers of adjacent teeth. The lengthy archwire span that exists between single brackets allows lower magnitude forces to be applied to the teeth over longer periods of time as compared to circumstances where the interbracket width is limited and the archwire span is short as is the case when conventional twin brackets are employed. The long span of archwire may be twisted much further without exceeding the elastic limit of the archwire material and causing permanent yielding or deformation of the archwire. Where the archwire between brackets is of limited length, which is typical where twin brackets are employed with the edgewise technique, application of large magnitude forces to the teeth can occur with only minimal twisting or flexing of the archwire. Thus, after limited movement of the teeth occurs, the forces induced by the short archwire interbracket width dissipate quickly, thereby requiring frequent adjustment in order to maintain optimum force application for efficeint tooth movement. Of course, it is evident that frequent adjustment of orthodontic appliances necessitates frequent visits by the patient for adjustment of the orthodontic appliance and is disadvantageous to the patient. Such frequent adjustment also requires a significant amount of chair time in the office of the orthodontist, thereby either increasing the cost of treatment to the patient, or minimizing the commercial advantage of orthodonitc treatment on the part of the doctor. It is desirable, therefore, to provide a system for orthodontic treatment wherein patient visits are minimized and chair time is also minimized, to the mutual benefit of both the patient and doctor.
Twin brackets for the edgewise technique have been employed for a considerable period of time. Twin brackets typically incorporate a pair of spaced projections that extend from or are formed by the bracket base, each projection being formed to define a precision active archwire slot segment. The spaced active archwire slot segments cooperate to define a precision archwire slot having the effect of extending the entire length of the base. Each of the projections is provided with upper and lower tie wings, thereby defining a bracket structure with four tie wings, the tie wings and the effective archwire slot terminating at the opposed side portions of the base structure. With the base structure centered in respect to the tooth to be moved, the tie wings will be positioned in pairs at opposed sides of the tooth, thereby defining bracket structure with efficient rotation control. The orthodontist may utilize ligature wire or elastic members between selected tie wings and the archwire to develop the force moments that are necessary for efficient rotational control.
One of the typical disadvantages in utilizing twin brackets is the minimization of interbracket width that exists as the result of positioning the tie wings at opposed side portions of the bracket structure. Ordinarily, as explained above, minimization of interbracket width, in conjunction with the edgewise orthodontic technique, suffers the disadvantage of requiring frequent patient visits and increasing chair time because of the necessity for frequent adjustment of the appliance in order to maintain the force levels within the optimum range for efficient tooth movement.
Another significant disadvantage of twin brackets is that the spaces that are typically available between the tie wings of adjacent brackets leave insufficient room between the teeth for closing loops and tie-back loops. It is desirable, therefore, to provide an orthodonitic bracket structure that affords the advantages offered by twin brackets and yet provides ample space between certain tie wings of adjacent brackets to facilitate efficient use of closing loops and tie-back loops in conjunction with edgewise orthodonitic therapy.